We have just got issue with WCAG compatibility when applying for WCAG certification.
 The problem is that RadCalendar used for RadDatePicker has a strange behaviour when tabbing. We can't get focus to buttons (<<,<, >, >>)  that are in the header of the Calendar popup. We can successively navigate contemt of the Callendar -days of the month both with Tab and arrow keys (with EnableKeyboardNavigation="true"
 ) , but not to header buttons.
 We found nearly the same problem on Telerik demo: http://demos.telerik.com/aspnet-ajax/calendar/examples/functionality/keyboardnavigation/defaultcs.aspx

 Please look that Calendar at the top of the page does not allow select its header buttons. But the one in popup inside RadDatePicker can tab to its header buttons. 
 (however in strange way order is: days navigation inside Calendar1 by arrows, Tab- RadCalendar1, Tab- header of Callendar1 first button: <<)